1. Field of the Invention
The present invention relates to a synchronous control method and a device of the same suitable for application to web-fed rotary printing presses.
2. Description of the Related Art
Conventionally, a synchronous drive control device for synchronously driving multiple web-fed rotary printing presses or multiple units (such as printing units or folding machines) in a web-fed rotary printing press has been configured to perform synchronous control even when the web-fed rotary printing press or the web-fed rotary printing presses are in shutdown as shown in Japanese Unexamined Patent Publication No. 2001-309681 (hereinafter, referred to as Patent Document 1), for example.
That is to say, Patent Document 1 relates to a synchronous control device applicable to web-fed rotary printing presses and the like, and more specifically, discloses an invention concerning a synchronous control device including a home position aligning function configured to accurately achieve synchronous drives of rotation phases and rotation speeds in terms of either electric motors including a main motor and a plurality of sub motors or respective machine shafts to be driven by the electric motors. Upon the synchronous control, firstly, phases of an electric motor shaft and the machine shaft of the main motor are constantly detected with a phase detector by use of an output from a rotary encoder of the main motor and an output from a main motor machine shaft home position detector. Meanwhile, phases of electric motor shafts and the machine shafts of the sub motors are constantly detected with phase detectors by use of outputs from rotary encoders of the sub motors and outputs from sub motor machine shaft home position detectors. Then, phase differences between the machine shaft of the main motor and the machine shafts of the sub motors are obtained by use of a machine shaft phase difference detector, and phase differences between the electric motor shaft of the main motor and the electric motor shafts of the sub motors are obtained by use of an electric motor shaft phase difference detector. Based on these outputs, home positions of the machine shafts of the main motors and the sub motors are aligned and then home positions of the electric motor shafts of the main motor and sub motors are aligned to perform synchronous control of the main motor and the sub motors.
However, the invention according to Patent Document 1 is configured to perform the synchronous control (position control and “0” speed control of the electric motors) even when the web-fed rotary printing presses are in shutdown. Accordingly, currents will flow on the electric motors and electric motor drive circuits even when the printing presses are in shutdown.
For this reason, this invention has problems of an increase in power consumption, and of deterioration in durability of the electric motors and bearings of the electric motors which are attributable to deterioration of greases of the electric motors of the bearings of the electric motors caused by heat generation.
Accordingly, the inventors and other people concerned of the present invention have found that the problems described above can be solved as shown hereinafter: speeds of respective web-fed rotary printing presses or respective units in a web-fed rotary printing press are detected; in conditions that the speeds are decreased until they reach a predetermined constant speed (for instance, 8 rpm) or are stopped based on a stop instruction, a phase of a virtual master generator is kept retained at the position and synchronous control of the respective web-fed rotary printing presses or the respective units is released; simultaneously drive motor brakes of the respective web-fed rotary printing presses or drive motor brakes of the respective units are activated; at least during the stop period of the respective web-fed rotary printing presses or the web-fed rotary printing press, rotations of the respective web-fed rotary printing presses or the respective units of a web-fed rotary printing press are stopped using both brakes of the drive motors; a deviation of the phases of the respective web-fed rotary printing presses or the respective units of a web-fed rotary printing press are prevented.
That is to say, during the stop period of the respective web-fed rotary printing presses or the respective units of a web-fed rotary printing press, it is not necessary to supply currents to the drive motors and to the drive motor drivers. Therefore, it is possible to reduce power consumption and to improve durability of the motors and motor bearings.
However, since rotations of the respective web-fed rotary printing presses or the respective units of a web-fed rotary printing press are stopped using both brakes of the drive motors, it is conceivable that malfunctions may occur, in other words, synchronous control will not be enabled in the subsequent operation in a case where the respective web-fed rotary printing presses and the respective units of a web-fed rotary printing press overrun by a large amount due to degradation and the like of the drive motor brakes and the web-fed rotary printing presses or in a case where the units are drove manually in maintenance or in adjustments of misaligned portions.